"We know clean energy is the ticket to strong, sustainable economic growth," Boxer, the chairwoman of the Environment and Public Works Committee, said at the Capitol Hill event, in front of a large American flag and three dozen or so military veterans, business leaders and environmentalists.

"Ultimately, this bill is about keeping Americans safe," added Kerry, the chairman of the Foreign Relations Committee.

The Kerry-Boxer bill (pdf), the "Clean Energy Jobs and American Power Act," comes in at 821 pages, starting with a mandate by 2020 to curb the nation's greenhouse gas emissions by 20 percent from 2005 levels. It omits many details, leaving negotiations with Democrats and Republican moderates to fill in the blanks.

But the measure offers specifics on several critical issues, ranging from incentives for natural gas and nuclear power to how Congress can promote tree planting and sustainable farming practices as alternative compliance options for industry.

The bill's sponsors also sought to change the legislative lingo surrounding the bill, dropping references to "cap and trade." Instead, Boxer and Kerry released a summary of their bill that labeled greenhouse gas trading provisions as a "Pollution Reduction and Investment" program. Boxer also touted a proposal allocating emission allowances that is aimed at fiscal conservatives who think past climate proposals cost too much.

"The bill does not add one penny to the deficit," Boxer said. "We're very excited about that."

The unveiling of the Senate climate bill comes almost three months after House passage of H.R. 2454, a comprehensive climate and energy bill that is a centerpiece of President Obama's domestic agenda.

"With the draft legislation they are announcing today, we are one step closer to putting America in control of our energy future and making America more energy independent," Obama said. "My administration is deeply committed to passing a bill that creates new American jobs and the clean energy incentives that foster innovation. I commend Senators Boxer and Kerry for their work and look forward to signing comprehensive energy legislation that addresses this urgent challenge."

Senior Obama administration officials are scheduled to meet later today with local elected officials from Maryland, Montana, North Dakota and Ohio who were in Washington to see the bill unveiled.

House Speaker Nancy Pelosi (D-Calif.), who was instrumental in moving the House climate bill before the July Fourth recess, called the Kerry-Boxer measure "a strong foundation for Senate action on our clean energy future."

"I look forward to working with my Senate colleagues to deliver to the President a comprehensive clean energy and climate bill as soon as possible to ensure the success of the Copenhagen negotiations," Pelosi said in a statement, referring to a major U.N. climate summit slated for the Denmark capitol in December.

House Republican leader John Boehner of Ohio was among the first to bash the Senate bill.

"The national energy tax was a terrible idea when it passed the House, and it is an even worse idea now," Boehner said in a press release. "Middle-class families and small businesses struggling to make ends meet shouldn't be punished with costly legislation that will increase electricity bills, raise gasoline prices and ship more American jobs overseas."

45 supporters and counting

Prospects for the Senate climate bill are uncertain.

Majority Leader Harry Reid (D-Nev.) earlier this month acknowledged the legislative reality that any unfinished business would not expire with the new year. And he told reporters yesterday that Democrats remain on track to move the legislation before the Copenhagen negotiations.

Senate Republicans critical of the climate bill do not think the Kerry-Boxer bill has enough legs to make it into law by Copenhagen. The Environment Committee's ranking member, Janes Inhofe (R-Okla.), said yesterday that he expects Obama to use House-passed legislation and a committee-approved bill as his main arguments at the U.N. talks.

There are 21 "fence sitters" pivotal to passing the bill. They include Democrats and Republicans who have offered positive statements about the legislative process, including Sens. Robert Byrd (D-W.Va.), Lindsey Graham (R-S.C.) and Debbie Stabenow (D-Mich.). Other lawmakers on that list -- Sens. Byron Dorgan (D-N.D.), Blanche Lincoln (D-Ark.), Lisa Murkowski (R-Alaska) and John McCain (R-Ariz.), for example -- have sounded recently like anything but cap-and-trade supporters.

Murkowski, the ranking member of the Energy and Natural Resources Committee, is scheduled to join several Senate GOP leaders and rank-and-file Republicans during an afternoon press conference billed as a chance "to discuss the national energy tax in the Boxer-Kerry bill."

Pennsylvania Democrat Arlen Specter, also a fence sitter, had originally planned to be at the Capitol Hill press conference but changed course to be at an event with Obama at the National Institutes of Health in Bethesda, Md.

The former Republican did release a statement that indicated he hopes to be on board when the climate legislation is finished.

"I support legislation to create clean domestic energy and address climate change in a way that is economically responsible, environmentally effective, and encourages action by other countries to achieve these goals," Specter said. "I believe the Kerry-Boxer bill can be structured, with committee and floor amendments, to meet these goals subject to the following considerations."

Specter then listed six provisions, including a "modified price collar" that gives "greater price certainty" than the House-passed legislation without busting the emissions cap; "the right combination of incentives and mandates" for commercial deployment of carbon capture and storage (CCS) technologies; advance payment of bonus allowances for qualifying CCS projects; "adequate allowances" for steel and other energy-intensive, trade-sensitive manufacturers; transportation provisions; and incentives for natural gas.

Environmentalists' reactions

Most environmental groups welcomed the legislation's introduction. "It's the starting gun in the Senate in a race that you can't afford to lose," said David Moulton, a former House aide to Rep. Ed Markey (D-Mass.) now working at the Wilderness Society.

"While the language the Senate unveiled today contains some improvements over the House bill, it fails to commit the U.S. to meaningful, science-based greenhouse gas emissions reductions needed to protect us from runaway climate change," Moglen said. "This proposal meets neither the needs of science nor those of the international community, which is currently negotiating the landmark climate treaty."

Senate sponsors insist that their emission targets, which are more aggressive than the 17 percent limit in the House bill, would be easier to meet because of the recent economic meltdown that has already led to lower emissions. Sanders, the Vermont senator, said during today's rally that he wants to strengthen the near-term emission targets.

The bill's emissions offset strategy also differs from the House-passed measure.

The Senate plan would states that three-fourths of the 2 billion tons of the annual offsets available to polluters would come from domestic projects and one-fourth from international efforts.

The House plan divided them evenly. An aide to Boxer said the higher domestic share in the Senate plan would help keep more investments in the United States.